1. Technical Field
The subject matter of the present disclosure relates to jet engines generally, and more particularly to certain new and useful advances in the manufacture, maintenance and/or operation of a segmented, deployable fan nozzle to reduce jet engine noise and fuel consumption.
2. Description of Related Art
Large turbofan engines with variable flow-path geometry afford attractive economic incentives because they reduce fuel consumption and engine noise. However, such engines require use of variable area fan nozzles (VAFNs) to keep critical fan parameters, such as pressure, speed and flow, within acceptable limits. Conventional VAFN's typically employ structure known by the aircraft industry as “chevrons” to attenuate engine noise. Triangular in shape and fixed in place, such chevrons are typically positioned along an aft edge of a secondary exhaust nozzle of the jet engine so that the chevrons project into the gas flow stream. Although this arrangement has been proven to reduce jet engine noise, the chevrons cause drag and loss of thrust because they dip into the fan stream. Accordingly, this loss of thrust must be balanced with the need to reduce noise.
At least two types of VAFN's have been developed. VAFNs with hydraulically-actuated chevrons are well-known, but are heavy and expensive to maintain. VAFN's using chevrons actuated by shape memory alloys (SMA's), such as the SMA chevrons designed and tested for the Quiet Technology Demonstrator (QTD) I and II programs, offer improved noise reduction, but their high-performance alloys, such as Nickel Titanium (NiTinol), are expensive. In the QTD II test, each chevron had a laminate construction. Three SMA strips of NiTinol were positioned on a base chevron formed of a composite laminate—two along the chevron's angled edges, and one extending from the chevron's tip to its center—and then covered with a cover plate. The SMA strips, which deformed in response to heat, bent each chevron inward during takeoff to reduce community noise and cabin noise. During cruise, the SMA strips straightened each chevron to reduce fuel consumption. In both applications, the base of the chevrons containing the SMA strips were immovable—e.g., did not translate forward or aft.
U.S. Pat. No. 6,718,752 to Nesbitt et al. illustrates an example of such chevrons in FIG. 21. This illustration identifies a known variable area fan nozzle (VAFN) 2100 having flow altering components 2102 that are bent and straightened by shape memory alloy (SMA) actuators.
Thus, nozzle chevrons that bend or “rotate” into and out of the stream offer some improvement over the fixed chevrons, but are still a compromise relative to aerodynamic performance of the nozzle. Accordingly, further improvements are desired that allow the geometry of the nozzle and exit area to be optimized, while providing improved acoustic attenuation, thrust and/or fuel efficiency.